Optical fiber connectors are an essential part of substantially any optical fiber communication system. For instance, such connectors may be used to join segments of fiber into longer lengths; to connect fiber to active devices such as radiation sources, optical amplifiers, detectors and repeaters; or to connect fiber to passive devices such as switches and attenuators. The central function of an optical fiber connector is the maintenance of two optical fiber ends such that the core of one of the fibers is axially aligned with the core of the other fiber; and consequently, all of the light from one fiber is coupled to the other fiber. This is a particularly challenging task because the light-carrying region (core) of an optical fiber is quite small. In singlemode optical fibers the core diameter is about 8 microns where 1 micron=1 .mu.m=10.sup.-3 mm. Another function of the optical fiber connector is to provide mechanical stability and protection to the junction in its working environment. Achieving low insertion loss in coupling two fibers is generally a function of the alignment of the fiber ends, the width of the gap between the ends, and the optical surface condition of either or both ends. Stability and junction protection is generally a function of connector design (e.g., minimization of the different thermal expansion and mechanical movement effects). An optical fiber connector typically includes a small capillary cylinder with a glass or plastic fiber installed along its central axis. This cylinder is interchangeably referred to as a ferrule or a plug.
In a connection between a pair of optical fibers, a pair of ferrules are butted together end-to-end and light travels from one to the other along their common central axis. In this conventional optical connection, it is highly desirable for the cores of the glass fibers to be precisely aligned in order to minimize the loss of light (insertion loss) caused by the connection; but as one might expect, it is presently impossible to make routine perfect connections. Manufacturing tolerances may approach "zero," but practical considerations such as cost, and the fact that slight misalignment is tolerable, suggest that perfection in such matters may be unnecessary.
One known design of an optical fiber connector is shown in U.S. Pat. No. 4,793,683; and its basic components comprise a precision molded plastic conical plug having an optical fiber centered therein, a compression spring disposed about a cylindrical portion of the plug, and a retention collar surrounding the plug and spring. The collar includes external threads that enable it to couple with another connector via a fixture having a precision molded alignment sleeve whose shape is best described as "biconic." This design has been superseded by the connector shown in U.S. Pat. No. 4,934,785 which comprises a cylindrical plug, a base member that holds the plug, a compression spring, and a cap that surrounds the plug and spring. In this design, only the cylindrical plug needs to be of high precision and is typically made from a ceramic material. When joining two of these plugs together, an alignment sleeve is used which comprises a split, thin-walled cylinder made of metal, ceramic or even plastic material. This alignment sleeve need not be as precise as the above-described biconic alignment sleeve.
And while the above connectors perform satisfactorily, further improvements are desirable. For example, because of the growing acceptance of optical fiber as the transmission media of choice for television, data, and telephone (multi-media) communications, the need to provide higher density interconnection arrangements has emerged. All of the above-mentioned simplex optical connectors are constructed in such a way that the ability to stack a large number of them together is limited by the need to manually grasp both sides during insertion and removal from a receptacle or coupling device. Known duplex optical connectors, such as the one shown in U.S. Pat. No. 4,787,706, also require manual access to the opposite sides of its housing during removal from the receptacle or coupling device which precludes high density optical fiber interconnection arrays. Furthermore, it is always desirable to reduce cost while still providing a connector that is immediately acceptable to customers. With these latter desires in mind, reference is made to the art of electrical connectors where, perhaps, the most used and accepted connectors are the ones known as RJ11-type plugs/jacks that are typically used in corded telephone products. These connectors have achieved widespread acceptance because they are inexpensive, they operate reliably, and their operation is readily understood by customers. However, because of the high precision and low insertion loss requirements associated with optical interconnections (particularly between singlemode fibers), RJ11-type designs have been unacceptable for optical connectors. Examples of such electrical connectors are shown in U.S. Pat. Nos. 3,761,869 and 3,954,320.
Another known design of an optical fiber connector is disclosed in U.S. Pat. No. 5,212,752. The optical connector comprises a ferrule assembly that includes a ferrule portion having a passageway for an optical fiber and a plug frame in which the ferrule assembly is disposed. Once the ferrule assembly has been disposed in the plug frame, the plug frame is assembled within another portion of the optical connector called a grip. The plug frame may be assembled within the grip in a plurality of rotational orientations with respect to the grip in such a way that the direction of eccentricity is aligned with a key of the grip. Once the plug frame has been coupled within the grip, the optical connector may be inserted into a coupling housing. The coupling housing is configured to allow two identical optical connectors to be inserted therein to provide an optical connection between two optical fibers terminated by ferrule assemblies within the optical connectors.
One of the advantages of the optical connector disclosed in U.S. Pat. No. 5,212,752 is that when the plug frame is inserted within the grip, the optical connector is provided with good side-loading characteristics due to the design of the grip and the manner in which the plug frame couples with the grip. One of the disadvantages associated with this optical connector is that, once the grip is installed, it cannot be removed. This is a disadvantage if, for some reason, tuning must be re-adjusted. The coupling housing is adapted to receive the grip. Although it may be possible to insert the plug frame into the coupling housing even when the plug frame is not disposed within the grip, removing the plug frame from the coupling housing once it has been inserted would be difficult, if not impossible without a special tool, due to the fact that there is no mechanism for detaching the plug frame from the coupling housing once it has been inserted. Furthermore, if the plug frame is not disposed within the grip, the side-loading characteristics of the optical connector are diminished.
Another disadvantage of this optical connector is that it is possible for certain components of the optical connector to be improperly assembled during the assembly process. This can be seen with reference to FIG. 2 of U.S. Pat. No. 5,212,752. A cable retention member is adapted to receive a barrel and spring of the ferrule assembly during the assembly process. The cable retention member includes a collar which is chamfered such that when the cable retention member is inserted within the plug frame, the side portions of the collar are received within windows of the plug frame. However, the plug frame has a cylindrical, or annular, opening that does not include any type of keying mechanism for ensuring that the side portions of the collar are received within the windows of the plug frame. Consequently, it is possible for the cable retention member to be pressed into the plug frame in such a manner that the side portions of the collar do not align with the windows. However, even if the side portions of the collar do not align with the windows, the cable retention member will be locked into place within the plug frame via a friction fit that makes it difficult, if not impossible, for the cable retention member to be removed from the plug frame. Therefore, improper assembly of the optical connector is possible if measures are not taken to ensure proper alignment of the cable retention member with the plug frame during assembly.
The improper assembly of the cable retention member within the plug frame prevents the optical connector from having a side-loading capacity that is as great as it would be if the side portions of the collar were properly seated within the windows of the plug frame. Also, once the cable retention member has been improperly inserted into the plug frame, it is difficult, if not impossible, to properly couple the plug frame with the grip, which will make it difficult, if not impossible, to couple the optical connector to the coupling housing in order to enable the ends of two optical fibers to be optically coupled together.
Another known design of an optical connector is shown in U.S. Pat. No. 5,481,634. This connector utilizes a two-piece housing assembly comprising a housing and a cover, which are ultrasonically bonded together after a ferrule and its associated components have been installed within the housing. The associated components comprise a fiber-holding structure that includes the ferrule, a base member and a spring that is disposed about the base member. The housing is a generally U-shaped device having a cavity for receiving the fiber-holding structure. Once the fiber-holding structure has been inserted into the cavity of the housing, the cover is bonded thereto. The cover includes pins that mate with holes in the housing for alignment. Once joined together by the pins and associated holes, the front end of the connector has a generally square shape that fits into a receptacle that is shaped to receive the connector. The connector has a spring latch molded thereto that includes a living hinge, which allows a tab to be moved up and down in a direction that is generally perpendicular to the axial passageway of the fiber-holding structure. The spring latch is used for securing the connector to the receptacle in order to prevent unintended decoupling of the connector and the receptacle.
Although the optical connector disclosed in U.S. Pat. No. 5,481,634 provides several advantages over the other connectors discussed above, such as, for example, facilitating insertion into and removal from receptacles in high-density environments, and preventing or minimizing alignment variations attributable to eccentricity, a need exists for an optical connector that improves upon the design disclosed in U.S. Pat. No. 5,481,634.
As stated above, the optical connector disclosed in U.S. Pat. No. 5,481,634 utilizes a two-piece housing assembly. The two-piece housing assembly comprises a housing and a cover that are coupled together via pins and associated holes. Once coupled together, the housing and cover are ultrasonically bonded together. The task of assembling the two-piece housing assembly in an automated manufacturing process presents significant challenges. Furthermore, utilizing a two-piece housing assembly requires that steps be taken to ensure that the coupling of the pieces of the housing assembly together is done in such a manner that the assembly is provided with sufficient side-loading capability.
Optical connectors must withstand at least a certain minimum amount of side-loading in order to operate properly. As is well known in the art, when optical fibers are bent beyond a particular bending radius, signal loss occurs. Therefore, an optical connector needs sufficient side-loading capability in order to prevent the optical fibers housed therein from being bent beyond an allowable bending radius. Although the optical connector disclosed in U.S. Pat. No. 5,481,634 provides adequate side-loading capability, ensuring that the optical connector is provided with adequate side-loading capability presents certain difficulties in the manufacturing process due to the fact that a two-piece housing assembly tends to be susceptible to side-loading problems at the locations where the pieces of the housing are coupled together.
Another popular design of an optical fiber connector is shown in FIG. 1. This connector 1 utilizes a two-piece housing assembly comprising a front plug body 2 and a rear extender cap 3 that has a metal insert-molded strength member (not shown). The plug body 2 has keyways 5-5 formed in opposite sides thereof. The rear extender cap 3 has keys 4-4 disposed on opposite sides thereof. The plug body 2 is coupled to the extender cap 3 by snapping the keys 4-4 located on each side of the plug body 2 inside of the keyways 5-5 formed in each side of the extender cap 3.
Although this optical connector provides several advantages over the other connectors discussed above, such as, for example, providing a substantially preassembled connector plug for installation on jumper cordage, a need exists for an optical connector that improves upon this connector design. The junction 6 where the plug body 2 and the extender cap 3 meet is susceptible to side-loading or side-pulling forces, which, as stated above, can cause the optical performance associated with the connector to deteriorate. There is a need to be able to increase the side-loads on the connector 1. However, doing so can cause the junction 6 to be flexed to unacceptable levels. It would be desirable to provide a connector that would not be flexed to unacceptable levels under increased side-loading conditions.
Accordingly, a need exists for an optical connector that has desirable side-loading characteristics, that is relatively easy to manufacture and assemble, and that is suitable for use in high-density applications where many optical connectors may need to be inserted into receptacles that are relatively close to one another in spatial proximity.